The present invention relates to transmissions and more particularly to a transmission that includes input and output cog assemblies in close proximity to each other and a derailleur that engages a chain linking the input and output cog assemblies on a low-tension side of the chain to laterally displace the chain between a pair of input and output cogs.
A common type of transmission is a bicycle transmission that typically includes a multi-chainring crankset or input cogs at the pedal or crank axis, a multi-sprocket cassette or output cogs at the rear wheel axis, and a drive chain connecting a selected chainring to a selected sprocket. Front and rear derailleurs are used to urge the drive chain between the various chainrings and sprockets, respectively, to achieve a desired gear ratio. One disadvantage with this configuration is that in order to achieve certain gear ratios, i.e. a large front chainring connected to a large rear sprocket or a small front chainring to a small rear sprocket, the chain must be oriented at extreme “crossover” angles. Crossover riding may cause undesirable rasping noises and premature wear of the chain as well as the crankset and the cassette. Another disadvantage of this transmission is a large amount of chain slack, resulting in chain suck, chain derailment and cog skipping. Yet another disadvantage of this transmission is that two shifters are needed to actuate the front and rear derailleurs. Further disadvantages are exposed shifting components and overlapping gear ratios. For example, a conventional twenty-four speed bicycle transmission has only thirteen unique gear ratios. Therefore, there is a need for a transmission that eliminates the above disadvantages.